Solid electrolytic capacitor and manufacturing method therefor

ABSTRACT

A solid electrolytic capacitor of the present invention includes a capacitor element having an anode member, a dielectric member, and a cathode member; an anode terminal attached to the anode member; a cathode terminal attached to the cathode member; and a housing for covering an outer periphery of the capacitor element, the anode terminal and the cathode terminal being each at least partly exposed from an undersurface of the solid electrolytic capacitor, the anode terminal having a projection formed by rolling using a roll having a large diameter portion and a small diameter portion, and being connected to the anode member at the projection.

FIELD OF THE INVENTION

The present invention relates to a solid electrolytic capacitor, and amanufacturing method therefor, which has an anode terminal or a cathodeterminal exposed to an undersurface thereof.

BACKGROUND OF THE INVENTION

A solid electrolytic capacitor structured as shown in FIG. 9 has beenconventionally known. This solid electrolytic capacitor includes acapacitor element 2 having an anode terminal 10′ and a cathode terminal12′ attached to an undersurface thereof. The capacitor element 2 iscovered with a housing 8 made of a synthetic resin. The capacitorelement 2 includes a dielectric oxide film 5, a cathode layer 6, and acathode lead layer 7, which are sequentially formed on a peripheralsurface of an anode element 3, which is a sintered body of a valvemetal. A valve metal means here a metal for forming an extremely fineand durable dielectric oxide film 5 by electrolytic oxidation treatment,and may be tantalum, niobium, aluminum, titanium, etc.

An anode lead 4 made of tantalum projects from the heightwise middle ofthe anode element 3. Because the anode lead 4 and the anode terminal 10′have a different height, a cylindrical bolster member 9 intervenesbetween the anode lead 4 and the anode terminal 10′ to electricallyconnect the both (see, for example, JP 2005-244177, A).

The arrangement of the bolster member 9 being attached on the anodeterminal 4 as described above however complicates the attachmentprocess, and requires high accuracy in attachment, because the bolstermember 9 has a small diameter and length of 1 mm or less. In order toavoid the process that is complicated and needs high accuracy, it ispossible to etch a metal plate to form a projection. However, lowetching accuracy in mass production could cause projections with greatvariations in height. This makes it difficult to attach the anode lead,entailing problems of poor appearance and performance variations.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention aims to providesolid electrolytic capacitors, and a manufacturing method therefor,which have anode terminals or cathode terminals with few variations indimension, as well as projections etc. that can be easily formed.

A solid electrolytic capacitor of the present invention includes acapacitor element having an anode member, a dielectric member, and acathode member; an anode terminal attached to the anode member; acathode terminal attached to the cathode member; and a housing forcovering the capacitor element, the anode terminal and the cathodeterminal each having an exposed surface exposed from an undersurface ofthe housing, the anode terminal having a projection formed by rollingusing a roll having a large diameter portion and a small diameterportion, and being connected to the anode member at the projection.

Another solid electrolytic capacitor of the present invention includes acapacitor element having an anode member, a dielectric member, and acathode member; an anode terminal attached to the anode member; acathode terminal attached to the cathode member; and a housing forcovering the capacitor element, the anode terminal and the cathodeterminal each having an exposed surface exposed from an undersurface ofthe housing, the cathode terminal having a recess formed on the exposedsurface by rolling using a roll having a large diameter portion and asmall diameter portion, the recess being filled with a synthetic resinincluded in the housing, the synthetic resin dividing the exposedsurface into a plurality of areas.

A solid electrolytic capacitor manufacturing method of the presentinvention includes the steps of:

producing a capacitor element having an anode member, a dielectricmember, and a cathode member;

producing an anode terminal and a cathode terminal from a metal platebefore or after the step of producing the capacitor element;

placing the capacitor element on the anode terminal and the cathodeterminal, connecting the anode member and a projection of the anodeterminal, and connecting the cathode member and the cathode terminal;and

coating the capacitor element on the anode terminal and the cathodeterminal with a housing,

wherein the projection of the anode terminal is formed at the step ofproducing the anode terminal and the cathode terminal by rolling themetal plate using a roll having a large diameter portion and a smalldiameter portion, and the anode terminal and the cathode terminal areeach at least partly exposed from an undersurface of the housing at thestep of coating the capacitor element with the housing.

Another solid electrolytic capacitor manufacturing method of the presentinvention includes the steps of:

producing a capacitor element having an anode member, a dielectricmember, and a cathode member;

producing an anode terminal and a cathode terminal from a metal platebefore or after the step of producing the capacitor element;

placing the capacitor element on the anode terminal and the cathodeterminal, connecting the anode member and the anode terminal, andconnecting the cathode member and the cathode terminal; and

coating the capacitor element on the anode terminal and the cathodeterminal with a synthetic resin to form a housing,

wherein a recess is formed on an undersurface of the cathode terminal atthe step of producing the anode terminal and the cathode terminal byrolling the metal plate using a roll having a large diameter portion anda small diameter portion, and the anode terminal and the cathodeterminal are each at least partly exposed from an undersurface of thehousing at the step of forming the housing, with the recess of thecathode terminal being filled with the synthetic resin, whereby theexposed surface of the cathode terminal is divided into a plurality ofareas.

The above solid electrolytic capacitor and manufacturing method thereforof the present invention enable the projection of the anode terminal forconnecting the anode member of the capacitor element to be formed withease and high accuracy, thereby improving productivity. In addition, theexposed surface of the cathode terminal on the undersurface of thecapacitor element can be easily divided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a rolling step of a solidelectrolytic capacitor manufacturing method of the present invention;

FIG. 2 is a perspective view of a metal plate rolled in the solidelectrolytic capacitor manufacturing method;

FIG. 3 is a perspective view showing an anode and cathode terminalsproducing step of the solid electrolytic capacitor manufacturing method;

FIG. 4 is a perspective view showing a capacitor element placing step ofthe solid electrolytic capacitor manufacturing method;

FIG. 5 is a perspective view showing a housing forming step of the solidelectrolytic capacitor manufacturing method;

FIG. 6 is a perspective view showing a cutting step of the solidelectrolytic capacitor manufacturing method;

FIG. 7 is a longitudinal sectional view of a solid electrolyticcapacitor produced by the solid electrolytic capacitor manufacturingmethod;

FIG. 8(A) and FIG. 8(B) are a sectional view and a back view,respectively, of a solid electrolytic capacitor produced in anotherembodiment; and

FIG. 9 is a longitudinal sectional view of a conventional solidelectrolytic capacitor.

DETAILED DESCRIPTION OF THE EMBODIMENT

As shown in FIG. 7, a solid electrolytic capacitor 1 manufactured by thepresent invention includes a capacitor element 2, an anode terminal 10and a cathode terminal 12 connected to the capacitor element 2, and ahousing 8 made of a synthetic resin for covering the capacitor element2. The capacitor element 2 includes a dielectric oxide film 5, a cathodelayer 6, and a cathode lead layer 7, which are sequentially formed on aperipheral surface of an anode element 3, which is a sintered body of avalve metal. The anode element 3 has an anode lead 4 made of tantalumand providing an anode member, which projects from the heightwise middleof the anode element 3.

Usable for the cathode layer 6 is a solid electrolyte made of aconductive inorganic material such as manganese dioxide, or a conductiveorganic material such as TCNQ complex salt and a conductive polymer. Thecathode lead layer 7 may be, for example, sequentially formed carbon andsilver layers, or a metal plating layer.

The anode element 3 may be in the form of a plate or foil other than asintered body. If a plate or foil made of a metal such as aluminum isused as an anode element, for example, then a portion thereof where nocathode layer is formed functions as an anode member, whereas the anodeelement 3 shown in FIG. 7 has the anode lead 4 projected therefrom. Thecathode layer 6 and the cathode lead layer 7 function as a cathodemember, and the dielectric oxide film 5 as a dielectric member.

The anode terminal 10 is formed from a base 10 a and a projection 10 b.The anode lead 4 of the capacitor element 2 is placed on the projection10 b. The anode lead 4 is connected to the anode terminal 10 byresistance welding, laser welding, or the like. A base material to beused for the anode terminal 10 and the cathode terminal 12 may be thesame material as conventionally used (an iron-nickel alloy, a copperalloy, etc.), but it is preferable from the viewpoint of workability andconductivity to use copper or an alloy mainly containing copper.

The capacitor element 2 is placed on the cathode terminal 12. Thecathode lead layer 7, which is a part of the cathode member of thecapacitor element 2, is connected to the cathode terminal 12 using aconductive adhesive such as a silver paste. The anode terminal 10 andthe cathode terminal 12 have an undersurface thereof exposed from anundersurface of the housing 8.

Now, an example of a manufacturing method for the solid electrolyticcapacitor of the present invention is described with reference to thedrawings. First, a metal plate 20 made of a copper alloy is rolled usinga rolling machine 30 shown in FIG. 1. The rolling machine 30 includes anupper roller 32 having a large diameter portion 32 a and a smalldiameter portion 32 b, and a cylindrical lower roller 31. The metalplate 20 is passed between the upper roller 32 and the lower roller 31to thereby provide a metal plate 20′, as shown in FIG. 2, formed with aprojection 10 b to be attached to the anode lead 4 and a tabular base 10a not to be in contact with the anode lead 4. The rolling is done suchthat the ratio of the thickness of the base 10 a and the projection 10 bin total to the thickness of the base 10 a only is 2:1.

Thereafter, as shown in FIG. 3, the metal plate 20′ is cut along a lineparallel with the projection 10 b extending direction to separate anodeterminals 10 and cathode terminals 12. At the same time, the metal plate20′ is blanked so as to define an outline of an anode terminal 10 and acathode terminal 12 of each capacitor element. A forward projectingportion 12 a projecting forward from the front end of the cathodeterminal 12, which is closer to the anode terminal 10, toward the anodeterminal 10 is formed above the level of the undersurface of the cathodeterminal 12, while a sideward projecting portion 12 b projectingsideward from the opposite sides of the cathode terminal 12 is formedabove the level of the undersurface of the cathode terminal 12.

Subsequently, as shown in FIG. 4, a plurality of capacitor elements 2are placed on the metal plate 20′, corresponding to respective anodeterminals 10 and cathode terminals 12. Each of the capacitor elements 2includes a dielectric oxide film, a cathode layer, which is a solidelectrolyte layer including polypyrrole, and a cathode lead layer, whichis carbon and silver layers, which are sequentially formed on a surfaceof an anode element made of a tantalum sintered body. A conductiveadhesive including a silver adhesive is applied on the cathode terminal12, on which the capacitor element 2 is placed to connect the cathodelead layer to the cathode terminal 12. The anode lead of the capacitorelement 2 is placed on the projection 10 b of the anode terminal 10 toconnect the anode lead to the anode terminal 10 by resistance welding.

Thereafter, each of the capacitor elements 2 is contained in a mold. Asynthetic resin is injected into the mold to cover the outer peripheryof the capacitor element 2 with a housing 8 as shown in FIG. 5. Theundersurface of the anode terminal 10 and the cathode terminal 12 isexposed from the undersurface of the housing 8. The anode terminal 10and the cathode terminal 12 also partly project from a lower portion ofthe opposite sides of the housing 8 in an arrangement direction of theanode terminal 10 and the cathode terminal 12 constituting each of thecapacitor elements (see FIG. 7). Finally, the metal plate 20′ is cut foreach of the capacitor elements to provide a plurality of solidelectrolytic capacitors 1 as shown in FIG. 6.

The solid electrolytic capacitor manufacturing method of the presentinvention would not need a step of attaching a bolster member to theanode terminal, as conventionally used, which requires high accuracy. Inaddition, according to the rolling step using the rolling machine 30including the upper roller 32 and the lower roller 31 as shown in FIG.1, it is possible to precisely define, with high accuracy, a dimensionof the metal plate 20′ after rolling shown in FIG. 2, that is, thethickness of the base 10 a and the height of the projection 10 b of theanode terminal 10 of the solid electrolytic capacitor shown in FIG. 7,from the diameter difference between the large diameter portion 32 a andthe small diameter portion 32 b of the upper roller 32 and the distancebetween both rollers 32, 31. Therefore, the projections have smallervariations in height than those of projections formed on the anodeterminal by etching or the like in the conventional manufacturingmethod. This provides excellent productivity.

Further, the productivity is superior to that of a method where theprojection is formed on the anode terminal by forging, with no physicalproblem such as damaging the anode terminal. That is, rolling would notsignificantly change the physical density of the anode terminal becausethe metal atoms are slid and rolled, but forging would increase thephysical load of the anode terminal and easily damage the anode terminalbecause the metal atoms are pushed into one another. Such a damage ofthe anode terminal would easily occur if the base material is forged tohalf of its thickness or less. Therefore, the anode terminalmanufacturing method by rolling of the present invention is particularlyeffective for anode terminals with a thickness of the base being ½ of orless than the total thickness including the projection.

FIG. 8(A) and FIG. 8(B) show another embodiment of a solid electrolyticcapacitor of the present invention. The embodiment has a plurality ofcathode exposed portions 12 d, 12 d on the undersurface of the solidelectrolytic capacitor 1, and forms a recess 12 c between these cathodeexposed portions 12 d, 12 d. The recess 12 c is filled with a syntheticresin included in the housing 8. In manufacturing the solid electrolyticcapacitor, the projection 10 b of the anode terminal 10 and the recess12 c of the cathode terminal 12 a can be formed at the same time byrolling a metal plate once. This can further improve the productivity.

The forward projecting portion 12 a and sideward projecting portion 12 bformed on the cathode terminal 12 in the above embodiment exert aneffect of preventing the cathode terminal 12 from getting away from thehousing 8 when subjected to an external force. Even if moisture caninfiltrate from the interface between the housing 8 and the cathodeterminal 12, the forward projecting portion 12 a and the sidewardprojecting portion 12 b will extend the infiltration route of water tothe capacitor element, exerting an effect of maintaining electriccharacteristics of the solid electrolytic capacitor.

The above description of the embodiments is to describe the invention,and should not be understood to limit the invention as claimed, or torestrict the scope thereof. The present invention is not limited to theforegoing embodiments in construction but can of course be modifiedvariously by one skilled in the art without departing from the spirit ofthe present invention as set forth in the appended claims.

1. A solid electrolytic capacitor comprising a capacitor element havingan anode member, a dielectric member, and a cathode member; an anodeterminal attached to the anode member; a cathode terminal attached tothe cathode member; and a housing for covering the capacitor element,the anode terminal and the cathode terminal each having an exposedsurface exposed from an undersurface of the housing, the anode terminalbeing formed by rolling and having a tabular base and a projectionprojecting from a surface of the base, the base extending out on eachside of the projection, the anode terminal being connected to the anodemember at the projection.
 2. The solid electrolytic capacitor accordingto claim 1, wherein the projection of the anode terminal projects towardthe opposite side to the exposed surface.
 3. The solid electrolyticcapacitor according to claim 1, wherein the projection of the anodeterminal is formed by rolling using a roll having a large diameterportion and a small diameter portion.
 4. The solid electrolyticcapacitor according to claim 1, wherein the anode terminal comprisescopper or an alloy mainly containing copper.